Interpretive Summary: The Wind Erosion Prediction System (WEPS) not only simulates soil erosion by wind, but also the degradation of soil roughness as influenced by precipitation and the decomposition of crop residue on agricultural fields. These WEPS components were tested using data measured on a farmer's field, planted with winter wheat, near Burlington, Colorado, USA. From November 2000 through April 2001, samplers were used to trap and measure wind blown sediment and automated devices detected the occurrence of saltating (bouncing) sediment.
WEPS overestimated the ability of small wheat plants to protect the soil against wind erosion. This component of WEPS is based on laboratory wind tunnel experiments with simulated standing biomass uniformly spaced on a flat surface. Wheat biomass in the field is not uniformly spaced. WEPS should be modified to account for these non-uniform realities. Differences between measured and simulated roughness degradation and residue decomposition were not significant, enhancing confidence in the ability of WEPS to simulate these processes.

Technical Abstract:
The Wind Erosion Prediction System (WEPS) includes submodels to simulate soil erosion by wind, roughness degradation and residue decomposition. These WEPS submodels were tested using data measured on a 600 m by 415 m farmer¿s field, planted with winter wheat, near Burlington, Colorado, USA. Big Spring Number Eight (BSNE) samplers were used to measure wind blown sediment flux and automated devices (Sensits) detected saltating sediment. A weather station recorded relevant meteorological data. Detailed measurements of field surface conditions were taken on three dates. One significant dust storm occurred during the experimental period (November 2000 through April 2001). Spatial variability of sediment discharge was high. This could partially be explained by spatial differences in residue cover and mass, leaf area index, sand fraction and wetness of the surface soil.
WEPS overestimated the ability of small wheat plants to protect the soil against wind erosion. A simulation without any wheat plants produced a large field sediment loss of 4.43 kg/m^2, whereas a simulation with only very small wheat plants (height = 10 mm, leaf area index = 0.1, stem area index = 0.01) produced no erosion. This component of WEPS is based on laboratory wind tunnel experiments with simulated standing biomass uniformly spaced on a flat surface. Wheat biomass in the field is not uniformly spaced. WEPS should be modified to account for these non-uniform realities.
Mean ridge height was reduced from 42 mm on 19 December to 34 mm (36 mm simulated using WEPS) on 12 April. Mean random roughness was reduced from 5.8 mm on 19 December to 5.2 mm (5.3 mm simulated) on 8 March. Mean corn residue biomass was reduced only slightly from 1204 kg ha-1 on 19 December to 1174 kg/ha^1 (1075 - 1175 kg/ha^1 simulated) on 12 April. These differences between measured data and simulations were not significant (P > 0.05), enhancing confidence in the ability of WEPS to simulate roughness degradation and residue decomposition.